Filtration of Broadly Graded Cohesive Dispersive Base Soils

Abstract

AbstractDispersive soils are highly susceptible to erosion, particularly when they are used as a base soil for the core of an earth dam. To prevent migration of the core material, the required filter must be designed and properly positioned in the structure. A study was carried out to assess the adequacy of the existing filter design criteria in controlling core materials that are not only dispersive but also broadly graded and are commonly available for use in the construction industry. The criteria of D15f/d85≤5.5 and D15f≤0.28 mm, each with a reasonable factor of safety, were found to be applicable for the broadly graded, highly dispersive soils from Group 1 and Group 2, respectively. The criteria of D15f/d85reduced≤9 for the soils of Group 1, D15f/d85reduced≤7 for the soils of Group 2 with significant clay content, and D15f/d85reduced≤2 for the soils of Group 2 with significant silt content were also found to be acceptable. Thus, the required D15f size of a filter reduces with the increasing dispersi...